Integrated circuits include many different devices, e.g., NFETs, PFETs, etc. integrated into a single chip or die. These integrated circuits can include, e.g., CMOS inverters, SRAM devices, etc. In CMOS inverters as in SRAM shared-gate devices, the NFETs and PFETs share a common gate-dielectric material, in addition to a common gate electrode. The workfunction metals, though, for a PFET and NFET may be different.
As the N-P boundary moves towards one or the other device, Vt dramatically increases at ground-rule proximities. For example, at about 30 nm distance of N-P boundary from the gate edges, the N-P local layout effect can account for approximately 30 mV of Vt increase (vs. isolated devices). This increase can be attributed to oxygen diffusion from the PFET side of the gate stack to the NFET side of the gate stack. The oxygen diffusion has a pathway with the common gate-dielectric material between the adjacent devices. That is, the common gate-dielectric material between the adjacent devices will act as a conduit for the oxygen transport from the PFET to the NFET.